Abstract:
Seed germination is strictly defined as the physiological events before radicle
protrusion through the endosperm cap, the endosperm region adjacent to the radicle tip.
There are two opposing forces governing seed germination: the growth potential of the
embryo and the mechanical resistance of the endosperm cap. The endosperm cap cell
wall is composed of galactomannan, which is degraded mainly by endo-β-mannanase.
LeMAN2 encodes an endo-β-mannanase which is induced by gibberellin (GA) during
germination. The upstream regulators of LeMAN2 are unknown in tomato. Using the
information available for GA-inducible transcription factors in Arabidopsis, tomato
orthologues of GA-inducible transcription factors were identified and characterized.
Four transcription factors are found to be expressed in germinating seeds. One of these
genes, GATA2 exhibited stage- and tissue-specific expression similar to that of LeMAN2.
GATA2 contains a GATA zinc finger domain similar to the zinc finger domain of AGP1
in tobacco which binds the AG motif in the promoter region of NtMYB2, a Myb protein.
An orthologue of NtMYB2 is expressed in tomato seed during germination. The tomato
GATA2 is hypothesized to be involved in the induction of LeMAN2 in an indirect manner
through the regulation of a Myb protein.
